The present disclosure relates to a semiconductor laser device to which semiconductor laser elements are attached and a cooling device used for the semiconductor laser device.
A semiconductor laser is used for a light source for a projector since light emitted therefrom has high straightness, has high brightness and high color purity. For example, JP 2011-165786A discloses that brightness of a display image is made high by arranging and using, as a light source for a projector, a plurality of semiconductor laser elements outputting light with the identical wavelength.
When a semiconductor laser is used for a light source for a projector, interference of light rays scattering on a screen with one another causes speckle noise, which is a fine dotted pattern, to be liable to arise, the speckle noise having been causing flickering on a display image.
The speckle noise is a phenomenon arising due to coherence of laser light and it is known that a measure for reducing the coherence of laser light is effective in order to reduce the speckle noise. The coherence of laser light is approximately in inverse proportion to its output spectrum width and the coherence is reduced when the output spectrum width of laser light is widened. Accordingly, widening the output spectrum width of laser light leads to reduction of the speckle noise.
JP 2011-165786A discloses, as a method for reducing the speckle noise, providing cooling parts for a pair of semiconductor laser elements, respectively, and controlling them so as to be different in cooling temperature at each cooling part. For a specific example of controlling them so as to be different in temperature, JP 2011-165786A discloses changing a cross-sectional area of a cooling medium channel inside each cooling part.